Patent GB-756529-A (GB)
Title: Apparatus for controlling a thermal de-icing system
IPC: B64D15/20
Filed: 1954-11-11
Abstract: 756,529. Switching systems for resistance heaters. NATIONAL RESEARCH COUNCIL. Nov. 11, 1954 [Nov. 25, 1953], No. 32723/54. Class 38 (4). [Also in Group XXXIII] Apparatus for controlling the de-icing of a surface comprises an ice detector (not shown) adapted to provide electric pulses under icing conditions, a timer connected to be initiated for a predetermined interval by a pulse from the detector and to be reinitiated by successive pulses, temperature control means for sensing the temperature of a parting strip of the surface, along which it is desired to part ice formed on the surface, the temperature control means being energized by the timer during said interval, a first heater located to heat said parting strip and controlled by the temperature-control means, a counter adapted to count the pulses from the ice detector, and a second heater located to heat an ice-shedding zone of the surface adjacent to the parting strip, and arranged to be energized when the counter reaches a predetermined count, and to remain energized for a predetermined time or until its temperature reaches a predetermined value. The timer 11 and the temperature-control means are shown in Fig. 1. A pulse from the ice detector on conductor 10 opens the contacts of relay 11 to de-energize the clutch coil 7, and move micro switch 5 to the position shown. With switch 9 inposition 2, current is fed through the contacts of relay 16 to the main heat-control relay (Fig. 2). The motor 6 also commences to run, and after a predetermined time, the micro switch 5 is moved to the off position. If a further pulse arrives on conductor 10 within this time, motor 6 is reset to run for the predetermined interval thereafter. The main heat control current 'can also be cut off by relay 16 controlled by the temperature controller 12 responsive to the resistance of an element 13 embedded in the parting strip. When its resistance increases to a preset value, relay 16 is operated. The resistance 13 is shunted by a resistance 14 and a thermal delay switch 15 so that for a brief period the parting strip may reach a higher temperature until switch 15 opens. A complete wiring diagram is shown in Fig. 2. When switch 61 is in the on position, pulses from the ice detector on line 21 are fed through the contacts of relay 47 to a relay 41 controlling the stepper relay 17 of a six-bank counter 42. With counter 43, this forms a counter adapted to give a signal when a count of ten, twenty ... sixty is reached, depending on the position of switch 44, the signal making line 18 live, through the contacts of a relay 48. On a count of nine, nineteen ... fifty-nine, bulb 52 lights up. Line 18 is connected to relays 47 and 45, which are energized (1) if a complete count is reached and (2) if relay 48 is not energized. A stepping switch 60 has two banks adapted to switch the temperature-sensing elements of eight parting strips to the temperature controller of Fig. 1 in turn. The third bank is adapted to energize relay 48 while the stepper 60 is not in its zero position, that is while a de-icing cycle is in progress. The fourth bank actuates the relay of stepper 60 when the temperature-sensing element in circuit has risen to its predetermined temperature or when the motor 6 has run for its predetermined interval. The fifth and sixth banks supply current to the shedding zone heaters, and reset switch 60 when it has completed its cycle. When a de-icing cycle by switch 60 is in progress, relay 48 is energized, and the resetting circuits of counters 43 and 42 are interrupted. When a complete count is reached, relay 47 is actuated to cut off pulses to relay 41, and thus the counter dwells at the final count. When switch 60 has finished its cycle, relay 48 is de-energized, and counters 42 and 43 reset themselves, and start counting again. Line 19 is thus made live if (1) a complete count has been reached, and (2) a de-icing cycle is not already in progress. Line 19 energizes a relay 62 and the stepper relay 20 of switch 60, to start the switch on its cycle. Relay 62 holds itself down, and holds relay 20 energized, until the predetermined interval elapses or the temperature controller of Fig. 1 is actuated. The relays 62 and 20 are then de-energized, and the relay 20 is energized again from the fourth bank of switch 60, advancing the switch a step. This is repeated until the switch 60 completes its cycle. A push button 46 can give the " count complete " signal manually through relay 49, and initiate a de-icing cycle if one is not already in progress. A bulb 53 lights up when the counters 42, 43 are dwelling on a completed count. Specification 739,527, [Group XX], is referred to.